Low freezing hydrazine based fuels

ABSTRACT

A rocket fuel having a freezing point below -65* F. consisting essentially of at least 23 percent by weight of hydrazine; 45 percent by weight of an alkyl hydrazine one from the group consisting of monomethyl hydrazine, symmetrical dimethylhydrazine and unsymmetrical dimethylhydrazine; and the balance being one from the group consisting of hydrazine nitrate, ammonium nitrate, ammonium perchlorate and carbon tetranitrite.

United States Patent Lum et al.

[151 3,658,609 [451 Apr. 25, 1972 [22] Filed:

[54] LOW FREEZING HYDRAZINE BASED FUELS [72] Inventors: Andrew F. Lum, Dover; Stanley Tannenbaum, Morristown, both of NJ.

[73] Assignee: The United States of America as represented by the Secretary of the Navy Dec. 28, 1961 [21] Appl.No.: 163,000

.... ..l49/36, 60/215, 60/218 ..C06d 5/08 ..l49/36; 60/354, 218, 215

[56] References Cited UNITED STATES PATENTS 7/1960 Rodrieth et a1. ..l49/36 52] US. Cl. [51] Int.Cl., [5 8] Field of Search 2,954,283 9/1960 Horwitz ..149/36 OTHER PUBLICATIONS Harshman Jet Propulsion" Apr., 1957 Primary Examiner-Carl D. Quarforth Assistant ExaminerE. A. Miller Attorney-Q. B. Warner and Arthur W. Collins [57] ABSTRACT 2 Claims, No Drawings This invention relates to hydrazine compositions and relates more particularly to hydrazine based fuels having extremely low freezing points.

For the past years hydrazine has received considerable attention as a liquid fuel propellantfor rocket engines. An ideal rocket fuel must havefour basic requirements: (1) high density, (2) low viscosity, (3) low molecular weight combustion products, and (4) low freezing point. Hydrazine has many superior properties including relatively high performance at low flame temperature, low molecular weight gaseous exhaust products and lack of solid products of its own decomposition which make it approach an ideal rocket fuel; however, its high freezing point (36- F.) will cause its solidification either at high altitudes or under severe weather conditions thereby destroying its usefulness as a fuel.

it is, of course, well known that the freezing or melting point of a compound is in general lowered by the inclusion therein of an impurity or other compound. In the past, this approach was taken in an effort to obtain a satisfactory freezing point i depressant for hydrazine with the subsequent expenditure of a tremendous amount of research.

One approach involved the dilution of hydrazine with water whereby a hydrazine-water mixture could be made so that the resultant system would retain the characteristics of hydrazine but have a freezing point of approximately -40 F. Although this mixture could function satisfactorily as a rocket fuel under the aforementioned atmospheric conditions of low temperature, it raised the equally important disadvantage of containing a relatively large percent by weight of non-combustible material.

To overcome this defect and still maintain a low freezing point mixture, hydrazine nitrate, which has the empirical formula N H .,NO has been a useful means of increasing performance and also lowering the freezing point. This fuel mixture possessed a high density, low viscosity and gave off cornbustion products of low molecular weight. The NzHgNoa acted as a substitute for water as a freezing point depressant.

for hydrazine. This depressant has a relatively high heat of combustion so that it was no longer a non-contributing component in the combustion process, as was water in hydrazinewater mixtures. In addition, the relative quantities of hydrazine nitrate required were less than the quantities of water required to effect a similar lowering in the freezing points of the resulting hydrazine compositions, thereby effecting proportionate reductions in space normally required for fuel storage and increasing the power obtainable per unit of fuel.

However, the addition of hydrazine-nitrate to hydrazine increases the thermal and shock sensitivity of the hydrazine as well as its performance, therefore, a balance had to be kept between the maximum concentration of the nitrate allowable for safety precautions and the minimum freezing point requirement. This balance was to maintain a mixture of 44 to 50 percent by weight of hydrazine nitrate whereby the freez-' ing point was approximately 40 F.

With the advent of space technology and the need for liquid propellants to have freezing points less than 65 F., a problem arose of how to make a hydrazine hydrazine nitrate mixture that could achieve these lower temperatures without the danger of explosion.

Therefore, an object of this invention is to provide a hydrazine based fuel which maintains its liquidity at temperatures below -65 F.

Another object of this invention is to provide for a freezing point depressant for hydrazine wherein the depressant will not lower the performance of hydrazine as a rocket fuel.

Another object of this invention is to provide a fuel mixture of hydrazine and hydrazine-nitrate displaying relatively good thermal stability toward shock at temperatures below --65 F.

Another object of this invention is to provide a high performance, low freezing hydrazine based rocket fuel.

Other ob ects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description.

in accordance with this invention, it has been found that the above objects and advantages can be obtained by providing as a fuel a mixture of anhydrous hydrazine, an alkyl hydrazine and an energetic oxygen containing compound which contains sufficient available oxygen to oxidize the carbon content of the alkyl hydrazine to carbon monoxide.

It has been discovered that the addition of an alkyl hydrazine from the group consisting of monomethylhydrazine, symmetrical dimethylhydrazine and unsymmetrical dimethylhydrazine to a mixture comprising hydrazine and one from a group consisting of hydrazine nitrate, ammonium nitrate, ammonium perchlorate and carbon tetranitrite effects an unexpectedly pronounced reduction in the freezing point of the mixture. This discovery is even more significant because the addition of the alkyl hydrazine and oxidizer to hydrazine does not appreciably reduce the overall performance of hydrazine as a rocket fuel.

The following hydrazine alkyl hydrazine system exhibited very good rocket fuel properties.

Hydrazine 24% by weight Monomethylhydrazine 45% by weight Hydrazine Nitrate 31% by weight This system freezes at 65 F. and it is practical storable and packageable fuel.

The weight of the hydrazine nitrate and the monomethylhydrazine is critical to the extent that there must be sufficient oxygen to oxidize the carbon in the monomethylhydrazine to CO.

While a specific composition and details have been set forth in the foregoing, it will be understood that various changes may be made without departing from the spirit and scope of this invention and that this invention is therefore not to be limited to such compositions and details except as set forth in the appended claims.

Having thus described the invention, what is claimed and desired to secure by Letters Patent is:

1. A rocket fuel having a freezing point below 65 F. consisting essentially of at least 23 percent by weight of hydrazine; 45 percent by weight of an alkyl hydrazine one from the group consisting of monomethyl hydrazine, symmetrical dimethylhydrazine and unsymmetrical dimethylhydrazine; and the balance being one from the group consisting of hydrazine nitrate, ammonium nitrate, ammonium perchlorate and carbon tetranitrite.

2. A rocket fuel having a freezing point of 65 F. consisting of 24 percent by weight of hydrazine 45 percent by weight of monomethylhydrazine 31 percent by weight of hydrazine nitrate. 

2. A rocket fuel having a freezing point of -65* F. consisting of 24 percent by weight of hydrazine 45 percent by weight of monomethylhydrazine 31 percent by weighT of hydrazine nitrate. 